Bantam Tools Blog

OtherYo: The Making of a Delrin Yo-Yo for String Tricks

Posted by Eric Chu on Aug 18, 2015 2:20:00 PM

Greetings from Other Machine Co.’s Design Studio! My name is Eric Chu and I’m an industrial design student at California College of the Arts spending the summer at OMC headquarters testing the limits of the Othermill.

Recently, I set out to make a Delrin plastic yo-yo on the Othermill. I’ve been calling it the OtherYo. It’s a modern ball bearing yo-yo designed for “string tricks,” the most popular style of yo-yoing, which involve having a long, spinning yo-yo that’s able to fit many layers of string in the gap of the yo-yo, where the ball bearing spins freely.

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The OtherYo consists of two identical halves with a ball bearing sandwiched in the middle and held together with a long set screw and two hex nuts. Two response pads surround the bearing and provide grip for the yo-yo string to wind up on. The two halves are concentrically aligned to the bearing seat so that when the yo-yo spins, there’s no vibration.

The common specs in today’s yo-yo design are:

  • 54.76mm diameter x 45.72mm width
  • 64g (roughly) in weight
  • “Slim pad” size groove for the response with a large (“C size”) bearing

The bearing presses onto the bearing seat and prevents accidental loss of the bearing but can be removed easily with a pair of pliers or a bearing-removal tool.

Why a yo-yo? Yo-yoing is one of my favorite hobbies. Not only is the yo-yo a fun toy to play with, but the yo-yo community is welcoming and I love seeing new products that yo-yo makers bring to market. Making a high-performance yo-yo has always been a dream of mine and of many yo-yo players. When I got to use the Othermill, I thought it was a great machine to get started with designing and making my own!

The design of the OtherYo was partially inspired by a very successful yo-yo, called the Project, made by One Drop Design. It was their first yo-yo and was actually made on their own CNC mill. The hex nut pocket was always a highlight of the yo-yo so I decided to incorporate it. The inner walls of the yo-yo were based on the YoYoFactory 888. Its accented rims allows the yo-yo to have a bit more weight on the rims for longer spins, and it adds a bit of flare to break the smooth domed surface.

R&D Process

While a yo-yo may seem like a relatively easy thing to mill, concentrically aligning the yo-yo’s two milling operations proved a bit challenging for me. I designed and experimented with many ways of securing the Delrin onto the bed of the Othermill.

My first jig used a C-clamp to hold the stock. The C-clamp tightened via a hex nut and screw that drops into milled out pockets. When the screw is tightened, the C-clamp pinches around the stock. It’s extremely secure and I’m even able to move and pick up the Othermill from the stock!

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The second jig that I made used the same hex nut and screw to actuate the clamp. This time it expanded and held a half-machined yo-yo from the inner rim. It was not as secure as the C-clamp jig (it could rotate if I turned it hard enough), so I used lighter cuts to prevent the part from being kicked off.

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The third jig required taping the yo-yo and getting rid of its hex-nut pocket. The jig had a raised ring that slotted into the response pad groove of the yo-yo. It had a press-fit to ensure the yo-yo would not go off center of the jig. The yo-yo screwed down onto the jig with a setscrew, providing the threads. This was by far the weakest of the jigs and the part actually unscrewed itself as the end mill cut its outer edge.

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Lastly, I’m working on a jig that’s similar to the second and third jigs but is way more secure and requires careful planning of the toolpaths. First, it’s bolted down directly to the T-slots of the bed to prevent any sort of movement caused by either the double-sided tape I used before or the natural bow of the HDPE sheet.

This fourth jig uses a solid extruded boss that the inner rim of the yo-yo is press-fit onto. A #2-56 socket-head machine screw locks the part down through the center hole of the yo-yo into a center hole on the boss. After milling all the features of the yo-yo, the screw is unscrewed and removed, and the bearing post of the yo-yo is machined with light cuts to achieve its proper height.

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Lessons Learned

The main issue that I ran into was not being able to concentrically align the yo-yo’s two milling operations, which is why I’ve iterated so many jigs! When the two operations aren’t aligned, the mass of the yo-yo is not radially equal to the spinning axis of the yo-yo, causing it to vibrate when it’s spun (think of pager motors or the vibration motors inside gaming controllers). The resulting yo-yo would vibrate so bad that it forms a ball of vibrating fury!

After many jig designs to try to solve the alignment issue, I found out that the cause of my issues were from my own user error in Fusion 360. I had set the offset of the model to a different value than my jig, so they were always 0.015" off in the y axis. This explains why my part always looked like it was way off when removed from the jig.

Speaking of user error, always double check your z offset when milling. I recommend setting a toolpath to slowly ramp down to the material before it cuts. That way this won’t happen:

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My z height had a different offset when I had changed jigs so the end mill drilled too far down the part and then rapidly to the side.

Also, bear in mind that milling Delrin can be quite messy.

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The fourth jig eliminates a lot of variables that could cause the alignment issues. Chances of the jig shifting and the HDPE bowing are greatly reduced. The design is better since it mounts the part more squarely and concentrically with less chance of it flexing while the part is being cut.

In the end, I learned that making a yo-yo and making the jig to hold the yo-yo both have unique challenges. It can take a lot of time and thinking to design a good jig to hold a part. There were a lot of challenges that I didn’t expect, and I now have a greater appreciation of machinists who work on these types of jobs!

After solving the alignment issue, a yo-yo half was milled with less than 0.002" misalignment, determined by measuring the rim of the yo-yo where the two operations meet.

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It works! Has a bit of a wobble but it plays quite nicely.

Now that I know there are no alignment issues, I’ll keep trying to improve on making a smoother spinning yo-yo by using a more solid jig made of aluminum.

I initially wanted to make a yo-yo with metal rims and a plastic body that press-fit together. I’ll work on that next, once I can consistently make smoothly spinning yo-yos!

Topics: Othermill Projects, Inside OMC, Fusion 360

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